Method and apparatus for determining the flangeability of sheet metal

ABSTRACT

A SHEET METAL FLANGEABILITY TESTER OVERFLANGES A SAMPLE AROUND CYLINDRICAL DIES HAVING PROGRESSIVELY CHANGING RADIUS. THE MAXIMUM RADIUS AT WHICH A FRACTURE OCCURS IN THE FLANGE IS A MEASURE OF FLANGEABILITY.

J. D. DANKOFF ET AL 3,566,680 METHOD AND APPARATUS FOR DETERMINING THE March 2, 1971 FLANGEABILITY OF SHEET METAL 5 Sheets-Sheet 1 Filed NOV. 29, 1968 l/VVE/VI'O/PS JOSEPH D. DAN/(OFF 8 ANDREW LESNEY By a C". .Mflnd Attorney March 2, 1971 J DANKOFF ETAL 3,566,680

METHOD AND APPARATUS FOR DETERMINING THE FLANGEABILITY OF SHEET METAL Filed Nov. 29, 1968 5 Sheets-Sheet l Mk2 IZUJ E: SL-303a INVE/V TORS JOSEPH D. DAN/(OFF 8 DREW LES/V5) Attorney March 1971 J. DQDANKOFF ETAL METHOD AND APPARATUS FOR DETERMINING THE FLANGEABILITY OF SHEET METAL 5 Sheets-Sheet 5 Filed NOV. 29, 1968 INVENTORS JOSEPH 0. DAN/(OFF 8 ANDREW LESWEY y a Z. M

Allarney March 2,1971 J DANKQFF ETAL 3,566,680.

METHOD AND APPARATUS FOR DETERMINING THE FLANGEABILITY OF SHEET METAL Filed Nov. 29, 1968 Sheets-Sheet 4 TTE-Ji.

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o l l l I I0 5 TEA IN INDEX INVENTORS JOSEPH D. DAN/(OFF 8 NDREW LESNEY A I Iomey March .2, 1971 J DANKOFF ET AL 3,566,680

METHOD AND APPARATUS FOR DETERMINING THE FLANGEABILITY OF SHEET METAL Filed Nov. 29, 1968 5 Sheets-Sheet 5 INVENTORS JOSEPHO. DAN/(OFF 8 SNEY ANDREW LE Attorney United States Patent 3,566,680 METHOD AND APPARATUS FOR DETERMINING THE FLANGEABILITY 0F SHEET METAL Joseph D. Dankofi, Derry Township, Westmoreland County, and Andrew Lesney, Frazer Township, Allegheny County, Pa., assignors to United States Steel Corporation Filed Nov. 29, 1968, Ser. No. 780,090 Int. Cl. G01n 3/28 U.S. Cl. 73-100 9 Claims ABSTRACT OF THE DISCLOSURE A sheet metal flangeability tester overflanges a sample around cylindrical dies having progressively changing radius. The maximum radius at which a fracture occurs in the flange is a measure of flangeability.

This invention relates to a method and apparatus for determining the flangeability of sheet metal and more particularly to a method and apparatus for measuring the tendency of tin plate to crack during flanging of can bodies.

Can bodies are made by first forming a hollow tube of sheet metal. Die plugs are then forced into each end of the can forming outwardly projecting flanges at right angles to the length of the can body. Gasket material is then applied to the can ends. A sheet metal end piece having a flange covering the body flange is then placed over the end of the body. Grooved rollers then curl the end and body flanges under and seaming rollers finally press the edges tightly together. Flanging the can body imposes a severe strain on the metal. If the strain is excessive, the metal fractures, resulting in defective cans when flanges split or crack.

The property of tin plate that largely determines flangeability is its ductility or ability to deform plastically during the flanging operation. Ductility can be measured by the elongation which a sample is capable of undergoing before fracturing in a tensile test. Because samples will neck down during a tensile test, the elongation must be determined in a gage length to include both the local elongation at the break and the uniform elongation in the remainder of the sample. A 2 gage length will provide an elongation indication, but a 0.05" gage length provides a better measure of elongation as related to flanging. Elongation tests require elaborate measuring and tensile testing equipment, particularly in a 0.05" gage length where photogridding and microscopic measuring are required. Elongation tests do not subject the metal to the same state of strain as actually occurs during a can flanging operation.

Bending a sample 180 and measuring the angle of spring back is another test used to determine flangeability but this is a measure of yield strength which is not necessarily a measure of flangeability.

Besides the physical properties of sheet metal, the flangeability of can body stock is also affected by the thickness of the stock, the width of the flange and the diameter of the cylinder around which the flange is formed. There are no tests that we are aware of that can correlate these factors in determining flangeability. There is also no simple test to compare flangeability of double reduced tin plate in a direction parallel to the direction of rolling with flangeability in a direction perpendicular to the direction of rolling.

According to our invention, a section of the tin plate to be used for can body is flanged between spiral shaped dies. The largest spiral radius at which a crack occurs is then used as a measure of the flangeability of tin plate.

It is, therefore, an object of our invention to provide a method of determining flangeability of sheet metal which 3,566,680 Patented Mar. 2, 1971 "ice uses the same forces as those in the intended service for the sheet metal.

Another object is to provide apparatus for testing flangeability of tin plate that is simple, inexpensive, quick, and requires little skill to perform.

Still another object is to provide such apparatus that will determine flangeability in a single test.

A still further object is to provide such apparatus that will determine a range of flangeability.

These and other objects will become more apparent after referring to the following specification and drawings in which:

FIG. 1 is an exploded perspectivve view of the three components of the flange former;

FIG. 2 is a perspective view of the outer die assembled over the inner die assembly with a test piece in position to be tested;

FIG. 3 is a sectional view along line III1II of FIG. 2 with a test piece in position after flanging and with the flanger between the jaws of a press;

FIG. 4 is a plan view of the inner die assembly of the preferred embodiment;

FIG. 5 is a perspective view of a strain index gage with a flanged test piece in the gage;

FIG. 6 is a chart showing the relation of the strain index to elongation in a 0.05" gage length;

FIG. 7 is a plan view of the inner die assembly of an alternate embodiment;

FIG. 8 is a sample shaped to give varying flange heights on a flanger with a circular shaped die; and

FIG. 9 is a plan view of the inner die assembly of another alternate embodiment.

Referring more particularly to the drawings, reference numeral 2 refers to a flange former. Flange former 2 consists of an inner die assembly 4, an outer die 6 and a pressure plate 8. Inner die assembly 4 has a base plate 10 and a vertical stop 12 at each corner. Two vertical alignment pins 14 project upwardly from base plate 10. An inner die 16 has a base 18 which is attached to base plate 10 by a retaining screw 20 at each corner and is aligned with the base plate 10 by two pins 22 projecting up from base plate 10 through holes in base 18. An inner die body 24 projects upwardly from base 18 with a connecting fillet 26 whose radius is the radius used in forming a can body flange. In the preferred embodiment shown in FIGS. 1, 2, 3 and 4, inner die body 24 has two connected spirals. As shown, a left spiral 28 has a radius increasing from about 0.56 inch to about 6.14 inches where it connects with a right spiral 30 which decreases from the 6.14 inch radius to a radius of about 0.87 inch. The working surface of inner die 24 is the outer vertical surface from a retaining slot 32 at the inner end of left spiral 28 to a retaining slot 34 at the inner end of right spiral 30. The upper portion of slots 32 and 34 are flared to facilitate placing the sample in the slots. Die body 18 has two hollows 36 to accommodate fingers for grasping the test piece when positioning and removing. To facilitate insertion of a sample, an indentation 38 is provided in the working surface approximately one third the distance from the top thereof.

Outer die 6 has two holes 40 therein to receive the vertical alignment pins '14 and a hole 42 that conforms to, but is slightly larger than, inner die body 24. The hole 42 has a rounded bottom edge 44 which matches the fillet 26 and an indentation 46 to match indentation 38.

Pressure plate 8 has four spring loaded supports pins 48 which rest on outer die 6 and support plate 8 above die 6.

A strain index gage 50, FIG. 5, has two supporting brackets 52 which are attached to a gage plate 54. Gage plate 54 has an opening 56 which conforms to the shape of outer die 6 but is reversed in a right and left direction. Strain index graduations 58 are located along the edge of opening 56 on both the large spiral and small spiral.

To test a sample, outer die 6 is placed over inner die assembly 4, and rests on vertical stops 12. A sample S, similar to a can body blank, 14% long and 2" wide is inserted in the space between the outer die 6 and inner die assembly 4. The length of the sample is such that its ends fit loosely within retaining slots 32 and 34 and its width is such that the desired flange width is obtained upon forming. The spacing between outer die 6 and inner die assembly 4 is suflicient for testing specimens having thicknesses between .0055 inch and .0099 inch without buckling the sample. The sample is inserted into the dies until it rests on fillet 26 with its top projecting above outer die 6 as shown in FIG. 2. Samples are easier to insert if precurled by passing through a conventional sheet metal roll former (not shown).

Pressure plate 8 is then placed over the assembled dies with the springs of support pins 48 holding plate 8 just off the top edge of the sample. The flange former is then placed in a conventional press 60 Which moves the pressure plate downward to force the specimen S into the cavity between the dies and form a flange as shown in FIG. 3. The spring loaded support pins 48 lessen the tendency of the upper edge of the sample S to flange outward along the top surface of outer die 6.

The strain in the flange depends on the radius around which it is formed, increasing from a minimum at the largest radius where the two spirals are joined to a maximum towards the inner end of each spiral. Thus in one flanged sample a range of gradually and continuously increasing strain is obtained sufficient to fracture the sample. The sample is removed from the flanger and placed in strain index gage 50. The largest radius at which a crack occurs, for example, at reference numeral 62 near graduation number 19 on FIG. 5, is a measure of the minimum strain at which a crack occurs. Cracks that occur at small radius locations such as those at reference numerals 64 are ignored.

In order to develop the scales shown in FIG. 5, a sample of annealed tin plate was first photogridded so that strains in a 0.05 inch gage length could be determined. Strains developed in the flanger are insuflicient to crack annealed tin plate. The sample was then flanged. Analysis of the photogridded flange disclosed a linear relation between the strains and the arcuate distance along the flange from the point of the largest radius, position in FIG. 5. This relation continues along the circumference of the larger spiral until near the location marked 29. The test area was terminated at this location because the free end of the sample, which is loosely contained in slot 34, disrupted the linearity. The markings O and 29 are arbitrary graduations which We call strain index. The higher the value of the strain index sustained by a sample without cracking, the greater the ductility of the material. The graduations 28 to 56 on the small spiral are a continuation of the same strain index, but the graduations are spaced closer because the spiral is smaller. Gage may be eliminated by placing index markings along inner die base 18, partially shown at reference numeral 66 in FIG. 4. Strain index is then determined before the sample is removed from inner die assembly 4.

The two spirals provide a range of strain index measurement in a single sample which is large enough to include most can sizes. FIG. 6 shows the relationship between the elongation in an 0.05 inch gage length and the strain index for a number of samples that were photogridded and tested in the flanger.

The tester was evaluated by testing a variety of samples of known flangeability, thereby establishing a range of strain index values to control material intended for can body fabrication. The tester also can detect the effect of changes in processing variables such as type of anneal prior to the second cold reduction, amount of the second cold reduction, and nitrogen content.

In the preferred embodiment of our apparatus for determining flangeability, the test was performed by flanging over a changing cylinder diameter. As long as the diameter becomes small enough the sample will fracture. However, since the flangeability also depends on flange 'width, the width of the flange may be increased beyond the width used in fabricating cans to insure the occurrence of a fracture. While it is preferred to use two connected spirals, a single spiral is adequate for a small testing range. FIG. 7 shows an inner die assembly with a single spiral shaped inner die 68, where the single spiral is adequate.

Flangeability can also be determined by holding the cylinder diameter constant and varying the flange width. Thus the flanger may have a circular shaped die 70 as shown in FIG. 9, and the flange width may be varied by using a sample tapered as shown in FIG. 8. A plurality of samples may also be flanged with successively increasing flange width until a fracture occurs. In this type of flangeability testing, the minimum flange width at which a fracture occurs is the measure of the flangeability of the metal. Such flanges do not have as large a test range because over flanging increases the problems of buckling.

The invention is also useful in determining flangeability and ductility of sheet metals other than tin plate used for can body stock such as aluminum. In addition, it could provide a measure of the characteristics of a laminate such as a paper backed foil.

While several embodiments of our invention have been shown and described, it will be apparent that other adaptations and modifications may be made.

We claim:

l. A method of measuring the flangeability of sheet metal which comprises the steps of transversely bending an elongated sample of the sheet metal into an arcuate shape, forming an outwardly extending flange along a longitudinal edge of the bent sheet, the ratio between the radius of bend and width of flange being varied along the length of sample, and determining the maximum ratio of radius of bend to flange width at which a fracture occurs in the sheet metal of the flange.

2. A method according to claim 1 in which the width of the tflange is larger than in the intended usage of the sheet metal thereby promoting the occurrence of a fracture.

3. A method according to claim 2 in which said arcuate shape is a cylinder, and said longitudinal edge i in the shape of an obtuse angle tapering uniformly from a maximum width in the center of the sample.

4. A method according to claim 2 in which said arcuate shape is a cylinder and in which a plurality of samples with increasing flange widths are measured.

5. A method according to claim 2 in which said arcuate shape is a cylinder with progressively changing radius along its length.

6. Apparatus for determining the flangeability of a sample of sheet metal which comprise an inner die having a curved surface thereon and a plane surface substantially normal to the curved surface extending outwardly therefrom, said curved surface having a progressively changing radius along it length, a fillet at the junction of said surfaces, an outer die surrounding said inner die, said outer die having surfaces thereon shaped to conform to the surfaces of the inner die, but with a substantially tion, said sections being joined along a common maximum radius of curvature to form a convex surface.

8. Apparatus according to claim 7 including means for indicating the maximum radius of curvature at which a fracture occurs, which means comprises a scale on said inner die plane surface, said scale having marks extending outwardly from the curved surface of the inner die a distance greater than the width of the flange on a sample, whereby a fracture location may be correlated with a mark when the outer die is removed.

9. Apparatus according to claim 8 in which said means for forcing a sample into the space between the assembled dies includes a pressure plate adapted to fit over the assembled dies and against the sample edge remote from said plane surface, a press adapted to exert force on said pressure plate, spring loading means for preventing said pressure plate from buckling said sample during the formation of a flange, and means for limiting the travel of the pressure plate to control the amount of sheet metal flanged.

References Cited UNITED STATES PATENTS 2,800,344 7/1957 Wolcott 72352X JERRY W. MYRACLE, Primary Examiner U.S. Cl. X.R. 72-352 

